Hybrid gas generator

ABSTRACT

The hybrid gas generator to inflate airbags comprises two combustion chambers ( 14, 16 ), in each of which a solid material charge ( 15, 17 ) is placed, and a storage chamber ( 11 ) containing a pressurized storage gas. The storage chamber ( 11 ) is connected to diffusion chamber ( 30 ) by a closing member ( 29 ) which can be perforated. The first solid material charge ( 15 ), and the second solid material charge ( 17 ) can, for instance, can be sequentially ignited by separate igniter elements ( 18, 19 ), thereby determining the pressure accumulation.

BACKGROUND OF THE INVENTION

The invention relates to a hybrid gas generator which contains anignitable, gas-generating solid charge and a storage chamber containinga gas.

A hybrid gas generator for air bags is known from EP 0 616 578 B1, whichcontains an ignitable solid charge in a combustion chamber and apressurized gas in a storage chamber. Upon the initiation of the gasgenerator, an ignition element ignites the solid charge. A hollow pistonis driven by the combustion gases which are generated, with the hollowpiston pushing through a closure element which closes the storagechamber, and with the pressurized gas contained in the storage chamberbeing able to flow out to the outlet. Moreover, the combustion gasesgenerated by the solid charge flow into the storage chamber, where theymix with the compressed gas. When the closure element is destroyed,first of all cold compressed gas flows to the outlet. This prevents thehot combustion gases from arriving in the air bag first. Subsequently, amixture of cold gas and combustion gas flows into the air bag.

Moreover, a hybrid gas generator is known from EP 0 669 231 A2, where amixing chamber is arranged between a combustion chamber containing thesolid charge and a storage chamber containing a compressed gas. Thecombustion chamber and the storage chamber are sealed by sealing discswhich are destroyed by the combustion gases of the solid charge. In thisrespect, the combustion gas and the cold gas penetrate from oppositedirections into the mixing chamber, with the flowing-out being impededas a result. Moreover, the hot combustion gas loaded with harmfulsubstances flows out initially because the sealing disc of thecombustion chamber is the first one to be destroyed.

The known hybrid gas generators have a pressure buildup behaviourdetermined by their construction, with the maximum pressure and thepressure increase gradient being specified. In the process, the air bagconnected to the gas generator is inflated very quickly and in one go.In the process, the passengers can be injured by the air bag if they are“out of position”.

SUMMARY OF THE INVENTION

The object of the invention is to create a hybrid gas generator whichmakes it possible to control the course of the pressure build-up withtime in order to effect greater safety for the passengers.

With the gas generator in accordance with the invention, two solidcharges are provided in different combustion chambers, with the secondsolid charge being ignitable in a time-delayed manner in relation to thefirst solid charge. In this way, the gas generation takes place with twodifferent pressure increase gradients, with preferably first of all arelatively flat pressure increase and then a steeper pressure increasebeing realized. The instant of the steeper pressure increase can bedetermined very accurately by the ignition delay. The two solid chargescan also be of different sizes or can provide different quantities ofgas. The percentage pressure distribution of the entire charge to thetwo individual charges makes a purposeful influencing of the pressurecharacteristic possible. Within the scope of the invention, it is evenpossible to provide, in addition to the two solid charges, at least onefurther solid charge.

The hybrid gas generator in accordance with the invention makes therealization of different types of pressure build-up characteristicspossible, indeed not only by means of the purposeful distribution of thecharges and the control of the ignition procedures, but also by means ofother structural modifications, for example the dimensioning of thecross section of the outflow openings.

According to a preferred development of the invention, the first solidcharge and the closure element are arranged at opposite ends of thestorage chamber, and the pushing element extends through the storagechamber. In this respect, the length of the pushing element can bevaried in order to realize different pressure build-up characteristics.A further parameter is the dwell time of the combustion gases in thestorage chamber before the closure element is opened. In this way, theheat transmission between the combustion gas and the storage gas can beinfluenced, this affecting the maximum pressure and the pressureincrease gradient.

Further advantages and features of the invention are evident from thefollowing description of various exemplifying embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, exemplifying embodiments of the invention will beexplained in more detail with reference to the drawings.

FIG. 1 shows a first embodiment of the gas generator in the stand-bystate.

FIG. 2 shows the gas generator according to FIG. 1 after theburning-away of the solid charges.

FIG. 3 shows a further embodiment of the gas generator with an annularsecond solid charge.

FIG. 4 shows an exemplifying embodiment where the solid charges arecoupled to each other pyrotechnically, so that the ignition takes placewith only one ignition element.

FIG. 5 shows an exemplifying embodiment with separate pushing elementswhich are allocated to the individual solid charges.

FIG. 6 shows a further exemplifying embodiment with a valve whichprotects the second solid charge against back-igniting when the firstsolid charge burns away.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the gas generator according to FIGS. 1 and 2 a tubular housing 10is provided, the interior of which forms the storage chamber 11. At theone end the housing 10 is sealed by a charge head 12 and at the oppositeend by a diffuser head 13.

The charge head 12 contains, next to each other, a first combustionchamber 14 with a first solid charge 15 and a second combustion chamber16 with a second solid charge 17. The solid charges 15, 17 arepyrotechnic charges. The solid charge 15 is allocated a first ignitionelement 18 and the solid charge 17 is allocated a second ignitionelement 19. The ignition elements 18, 19 are accommodated in the chargehead 12 and they project into the respective combustion chamber. Theignition elements can be electrically ignited by a control part (notshown). They contain a respective ignition charge which burns away andthereby ignites the associated solid charge 15 or 17.

The combustion chamber 14 has an outflow opening 20 leading into thestorage chamber 11, and the combustion chamber 16 has an outflow opening21 which likewise leads into the storage chamber 11. A perforated disc22 or 23 which keeps back the solid charge is arranged in front of therespective outflow opening 20 or 21 in the interior of the respectivecombustion chamber. The perforated discs 22, 23 are to keep back thesolid particles when the solid charges burn away, until completecombustion has taken place. Moreover, the outflow opening 21 is sealedby a membrane or bursting disc 24 which is likewise destroyed or openedby way of the gas pressure.

The storage chamber 11 contains a pressurized storage gas. A pushingelement 25 in the form of a rod extends through the storage chamber, thepushing element being provided at the end facing the combustion chamber14 with a cap 26 covering the outflow opening 20 and having a plunger 27at the opposite end. The plunger 27 is guided in a tube guide 28 of thediffuser head 13. The tube guide 28 is sealed by a closure element 29which the plunger 27 can push through or push off in order to open thepassage from the storage chamber 11 to the diffuser chamber 30 containedin the diffuser head 13. Outflow openings 31 lead from the diffuserchamber 30 into the area surrounding the housing 10, with the area beingconnected to the air bag (not shown).

In the event of initiation, first of all the ignition element 18 iselectrically ignited, which for its part ignites the first solid charge15. As a result of the pressure of the combustion gases, the pushingelement 25 is axially moved in order to push open the closure element29. The hot combustion gases flow from the combustion chamber 15 intothe storage chamber 11, where they mix with the cold storage gas. Thegas mixture flows into the diffuser chamber 30 and out of the latterthrough the outflow openings 31. After the initiation of the firstignition element 18 the second ignition element 19 is electricallyinitiated, even before the pressure in the storage chamber 11 hasdeclined. A steep pressure increase is produced by way of theburning-away of the second solid charge 17, with the steep pressureincrease being attributable to the fact that both solid charges 15, 17now burn away simultaneously. The pressure characteristic and the valueof the maximum pressure reached and the instant of the steeper pressureincrease are determined by means of the two solid charges 15, 17, thequantities of which are coordinated with each other, and by means of thetime-delayed ignition of the solid charges. The instant when the closureelement 29 is pushed open is determined by the length of the pushingelement 25. Furthermore, the heat transmission between the combustiongas and the storage gas is influenced by the residence time of the hotcombustion gas of the storage chamber 11 before the closure element 29is pushed open, this affecting the maximum pressure and the pressureincrease gradient.

FIG. 2 shows the end state of the hybrid gas generator after theburning-away of both solid charges. The plunger 27 with the closureelement 29 is now located in the diffuser chamber 30, and all outflowopenings 20, 21 and the tube guide 28 are open.

Whereas in the first exemplifying embodiment the two solid charges arearranged next to each other, in the exemplifying embodiment of FIG. 3the second solid charge 17 is contained in an annular combustion chamber16 which surrounds the centrally arranged combustion chamber 14. Theoutflow opening 20 of the first combustion chamber 14 is arranged alongthe central axis of the storage chamber 11. The annular secondcombustion chamber 16 has outflow openings 33 which do not lead into thestorage chamber 11, but are directed radially to the outside so that theescaping hot gas flows directly into the area surrounding the housing 10and mixes there with the remaining gas mixture which has issued from thediffuser chamber 30. Filters 34 in front of the radial outflow openings33 are to keep back the solid particles of the solid charge untilcomplete combustion has taken place.

As a result of gas pressure, the combustion gas of the solid charge 15separates the connection between the container 10 and the cap 26 at apredetermined breaking point, so that the combustion gases enter intothe storage chamber 11. Here they mix with the storage gas, and the gasmixture flows into the diffuser chamber 30. After the ignition of thefirst solid charge 15, the second solid charge 17 is ignited in atime-delayed manner.

In the exemplifying embodiment of FIG. 4 only the first solid charge 15is coupled to an ignition element 18. The two combustion chambers 14, 16are connected to each other by way of a bridge 34. The bridge 34 cancontain a pyrotechnic delay line, a heat-transmitting wall part or awall which can be destroyed when the solid charge 15 is burned away.During the burning-away of the first solid charge 15, the thermal orpyrotechnic ignition of the second solid charge 17 takes place by way ofthe bridge 34. The advantage of this variant lies in that only anelectrical signal has to be emitted to the gas generator. The ignitionelement 19 in FIG. 4 can therefore be dispensed with. However, if theignition element 19 is present, optionally the one or the other ignitionelement 18, 19 can be activated first of all, so that, depending on theignition element which is actuated, another characteristic of thepressure distribution is obtained.

In the exemplifying embodiment of FIG. 5, two solid charges 15, 16 ofdifferent sizes are provided, each of which has its own ignition element18 or 19. As in the first exemplifying embodiment, the first solidcharge 15 drives a pushing element 25, and the second solid charge 17 isallocated a further pushing element 35 which leads through the storagechamber 11 and covers the outflow opening 21 with a cap 36. At the endof the second pushing element 35 there is a plunger 37 for pushing opena closure element 39 which seals the storage chamber 11 against thediffuser chamber 30. Either of the two solid charges 15, 16 can be thefirst one to be ignited, and the other solid charge is thereafterignited after a certain delay. The solid charge which ignites firstopens the relevant closure element 29, 39 of the storage chamber 11. Thegas mixture is additionally heated by the solid charge which is ignitedlast.

In the exemplifying embodiment of FIG. 6, likewise each of the two solidcharges 15, 17 is allocated its own ignition element 18, 19. The outflowopenings 20, 21 lead into a collecting chamber 40 which is connected tothe storage chamber 11 by way of an outflow opening 41. The outflowopening 41 is covered by the cap 26 which is connected to the pushingelement 25. As a consequence of the collecting chamber 40 it ispossible, by using a single pushing element 25, to ignite either of thetwo solid charges 15, 17 first as a matter of choice. Because theexplosive charges have different sizes and/or different structures, thepressure generation characteristics can be selected by means of suitableactivation of the ignition elements 19, 20.

The collecting chamber 40 contains a valve 42 in the form of a shutter,which can be pivoted about an axis 43. If the solid charge 15 is ignitedfirst, the valve 42 in front of the outflow opening 21 of the othersolid charge 17 shuts, in order to prevent this solid charge 17 frombeing ignited by the collecting chamber 40. If, on the other hand, thesolid charge 17 is ignited first, the valve 42 in front of the outflowopening 20 of the other solid charge 15 shuts.

What is claimed is:
 1. Hybrid gas generator with a first solid chargearranged in a first combustion chamber, a storage chamber containing acompressed gas, which storage chamber is sealed by a closure element,and a pushing element pushing open the closure element under thepressure of the combustion gases, characterized in that a secondcombustion chamber is provided, which contains a second solid charge,which is ignitable in a time-delayed manner in relation to the firstsolid charge, the two combustion chambers being connected to acollecting chamber which has an outflow opening connected to the pushingelement, with each of the solid charges being provided with its ownignition element, and that solid charge which is to burn away firstbeing able to be selected by the activation of the relevant ignitionelement.
 2. Hybrid gas generator according to claim 1, characterized inthat the first solid charge and the closure element are arranged atopposite ends of the storage chamber, and the pushing element extendsthrough the storage chamber.
 3. Hybrid gas generator according to claim1, characterized in that a valve is provided, which protects the secondsolid charge against back-igniting when the first solid charge burnsaway.
 4. A hybrid gas generator comprising: a storage chamber containinga compressed gas, the storage container being sealed by a closureelement; a first combustion chamber containing a first solid charge andhaving a first outflow opening for releasing combustion gases; a secondcombustion chamber containing a second solid charge and having a secondoutflow opening for releasing combustion gases; means for igniting thesecond solid charge in a time-delayed manner in relation to the firstsolid charge; a collecting chamber connected to the first and secondoutflow openings and having an outflow opening; and a pushing elementprovided between the outflow opening of the collecting chamber and theclosure element of the storage chamber for pushing open the closureelement under pressure of combustion gases.
 5. A hybrid gas generatoraccording to claim 4, wherein the means for igniting the second solidcharge in a time-delayed manner in relation to the first solid chargecomprises a first ignition element for igniting the first solid chargeand a second ignition element for igniting the second solid charge.
 6. Ahybrid gas generator according to claim 5, wherein the means forigniting the second solid charge in a time-delayed manner in relation tothe first solid charge further comprises a valve movable between aneutral position, a position closing the first outflow opening of thefirst combustion chamber in response to combustion gases released firstfrom the second combustion chamber and a position for closing the secondoutflow opening of the second combustion chamber in response tocombustion gases released first from the first combustion chamber.